HTML5 video wasn't uniformly supported across browsers (and remember Google announced Chrome would drop h.264 around that time) and I didn't get positive responses on the idea. Maybe with more tools to support HTML5 video in animated GIF use cases and educational tools showing the difference in loading times and encoding algorithms this idea could take hold.
Also the WebP engineers have developed an animated WebP format which I disagree with but could be a step toward breaking GIF's monopoly on short animations.
It's still the case, IMHO. For example, mobile devices are a lost battle, in my experience, when it comes to HTML5 video (with autoplay and without controls). So MC ends up serving the straight up GIF to them.
I hope animated WebP becomes a thing but I have my doubts. I'm not sure whether the three major browsers will support it to an extent that it's actually sensible to use animated webp.
A good animated picture format could be similar in size to video, while maintaining the advantages of a gif.